wchar_t*, char* and perl XS

[xiaoyafeng]

Hi, monks

I've been writing a watchdog with Win32::Process::List. the script itself is extremely simple, monitor processes running and spawn a new one if the process which was monitor quit.

the interesting is where I browse in the W::P::L XS code

..........
pe32.dwSize = sizeof( PROCESSENTRY32 );
        if( !Process32First( hProcessSnap, &pe32 ) )
        {
            printError(wszMsgBuff,&err );
            sv_upgrade(perror,SVt_PVIV);
            sv_setpvn(perror, (char*)wszMsgBuff, strlen(wszMsgBuff));
            sv_setiv(perror,(IV) err);
            SvPOK_on(perror);
            XPUSHs(sv_2mortal(newSViv(-1)));
            CloseHandle( hProcessSnap );
        } else
        {
              do
              {
                  sprintf(temp, "%d", pe32.th32ProcessID);
                  if(debug==1) {
                      printf("Temp: %s\n",pe32.szExeFile);
                  }
                  
                  if(hv_store(rh,temp,strlen(temp),newSVpv(pe32.szExeF
+ile, strlen(pe32.szExeFile)), 0)==NULL)
                  //if(hv_store(rh,pe32.szExeFile,strlen(pe32.szExeFil
+e),newSVuv(pe32.th32ProcessID), 0)==NULL)
                  {
                      printf("can not store %s in hash!\n", pe32.szExe
+File);
                      
                  }
              } while( Process32Next( hProcessSnap, &pe32 ) );
            CloseHandle( hProcessSnap );

.....

and here is the definition of structure PROCESSENTRY32

typedef struct tagPROCESSENTRY32 {  
DWORD dwSize;  
DWORD cntUsage;  
DWORD th32ProcessID;  
ULONG_PTR th32DefaultHeapID;  
DWORD th32ModuleID;  
DWORD cntThreads;  
DWORD th32ParentProcessID;  
LONG pcPriClassBase;  
DWORD dwFlags;  
TCHAR szExeFile[MAX_PATH];
} PROCESSENTRY32,  *PPROCESSENTRY32;

As above szExeFile is a TCHAR arary, and actually, in my computer, it's a WCHAR array. the author of W::P::L put a wchar_t into a sv directly by sv_setpv. and it seems right when I check typemap under ExtUtils:

wchar_t *        T_PV
.......
.......
T_PV
    sv_setpv((SV*)$arg, $var);

But wield is, when I put the similar c code in VS2010, it complains:

: error C2664: 'Perl_sv_setpv' : cannot convert parameter 3 from 'WCHA
+R [260]' to 'const char *const ' (I think it more makes sense tho)

So what is perl/XS does to make building this module correctly?